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High- p T Results from STAR

STAR. High- p T Results from STAR. Carl A. Gagliardi Texas A&M University for the Collaboration. Introduction Spectra Elliptic flow Correlations ( Δφ and Δη ) Forward physics. STAR. Pedestal&flow subtracted. What We Know – Jet Quenching .

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High- p T Results from STAR

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  1. STAR High-pT Results from STAR Carl A. Gagliardi Texas A&M University for the Collaboration • Introduction • Spectra • Elliptic flow • Correlations • (ΔφandΔη) • Forward physics

  2. STAR Pedestal&flow subtracted What We Know – Jet Quenching Phys. Rev. Lett. 91, 072304 (2003). Inclusive yields and back-to-back di-hadron correlations are very similar in p+p and d+Au collisions Both are strongly suppressed in central Au+Au collisions at 200 GeV

  3. What We Know – Baryon Enhancement Clear meson-baryon yield differences at intermediate pT They seem to come together at pT ~ 5-6 GeV/c

  4. Identified Strange Particles in 200 GeV d+Au STAR Preliminary Yields to ~ 5 GeV/c measured vs centrality

  5. Meson-Baryon Difference in d+Au 200 GeV RCP also shows a clear meson-baryon pattern in d+Au

  6. STAR Pseudo-rapidity Density in d+Au PRC 70, 064907 Particle yields are consistent with a range of models

  7. STAR Pseudo-rapidity Yield Asymmetry vs pT Au direction / d direction PRC 70, 064907 Back/front asymmetry in 200 GeV d+Au consistent with general expectations of saturation or coalescence; doesn’t match pQCD prediction. See talk by Zhangbu Xu, Friday.

  8. π0 pT Spectrum in 200 GeV d+Au PHENIX data: PRL 91, 072303 (2003) Neutral pion pTspectrum to 13-16 GeV/c Reasonable agreement with pQCD calculation, STAR charged-hadrons, and PHENIX neutral pions Still working on energy scale at high pT

  9. Au+Au at 62 GeV: Charged-Particle Yields Spectrum shapes similar, but high-pT absolute yield down over an order of magnitude at 62 GeV relative to 200 GeV

  10. STAR Inclusive Hadron Suppression • 2 h bins, driven by p+p • h = 0: pT <~6 GeV • h = 0.7: pT <~10 GeV • Significant suppression seen at 62 and 200 GeV 200 GeV |h| < 0.5 62 GeV |h| < 0.5 62 GeV 0.5 < |h| < 0.9

  11. STAR RCP: Centrality Dependence • Significant suppression in both η regions • 62 GeV η ~ 0.7 very similar to 200 GeV η ~ 0 RCP 62 GeV |h| < 0.5 62 GeV 0.5 < |h| < 0.9 200 GeV |h| < 0.5

  12. Log10(dE/dx) Log10(p) Additional Particle Identification Techniques • TOF using MRPC chambers • π0conversion intoe+e-e+e- • dE/dxrelativistic rise

  13. Charged and Neutral Pions in 62 GeV Au+Au Three different techniques – good agreement

  14. p Nuclear Modification Factor • RCP for h+- 20% higher than p+- for pT = 3-4 GeV/c • RCP for h+- and p+- merge at pT = 5~6 GeV/c See talk by Zhangbu Xu, Friday

  15. M. Gyulassy, I. Vitev and X.N. Wang Azimuthal Anisotropy and Partonic Energy Loss Anisotropy at high pT is sensitive to the gluon density of the medium.

  16. STAR Separating Flow from Non-Flow at 200 GeV PRL 93, 252301

  17. STAR Flow at High pT in 200 GeV Au+Au PRL 93, 252301 v2 {2-particle} v2 {AuAu – pp} v2 {4-particle} Flow reaches a maximum ~3 GeV/c, then decreases slowly Sizable real flow to ~8 GeV/c in mid-central collisions

  18. STAR Flow in 62 GeV vs 200 GeV Au+Au Preliminary Upper curves: v2 {2-particle} Lower curves: v2 {4-particle} Solid points: 62 GeV Open points: 200 GeV v2(pT) is very similar for 62 GeV to 200 GeV

  19. STAR Back-to-Back Correlations vs. Reaction Plane PRL 93, 252301 20-60% central Near-side correlations: independent of orientation Back-to-back correlations: suppressed more strongly when the path length is longer

  20. STAR Di-Hadron Angular Distributions:62 GeV vs 200 GeV Au+Au Near: |Δφ| < 0.8 Away:|Δφ-π| < 0.8 STAR Preliminary STAR Preliminary Near-side correlated yields are much reduced at 62 GeV Away-side angular distribution is very similar

  21. meson – π, K baryon – p, p STAR vs PHENIX  correlations in Au+Au PHENIX nucl-ex/0408007 • Difference in STAR/PHENIX yields due to various |η| windows • Significant increase of the near-side yield in mid-central Au+Au collisions in comparison to p+p and d+Au |η|<0.7 |η|<0.35 STAR preliminary See talk by Ying Guo, tomorrow

  22. STAR p+p Jet-like structures (1/Ntrig) dN/d(Df) Signal Au+Au top 5% background Df Finding the Associated Hadrons nucl-ex/0501016 See talk by Fuqiang Wang, today Explores the interaction of an energetic parton with the dense medium

  23. STAR STAR, PRL 90 (2003) 082302 What about the near-side yield? PRL 90, 082302 STAR nucl-ex/0501016 A discrepancy?

  24. p+p minbias Au+Au, 20-40% STAR preliminary What might we learn with  correlations? • Azimuthal correlations hampered by v2 • v2 affects both yield, width determination • Background normalization difficult •  cleaner observable for both • STAR → large acceptance enables multi-differential study

  25. p+p 200 GeV: Near-Side,  vs  3 < pT(trig) < 4 GeV 4 < pT(trig) < 6 GeV 6 < pT(trig) < 12 GeV Consistent ,  evolution with pT(trig) || < 0.7 STAR preliminary || < 0.7 2 < pT(assoc) < pT(trig)

  26.  : System, Centrality Dependence at 200 GeV Au+Au: peak broadens, height drops with centrality STAR preliminary 3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig) || < 0.5

  27. STAR preliminary 6 < pT(trig) < 12 GeV  : System, Centrality Dependence at 200 GeV 2 < pT(assoc) < pT(trig) || < 0.5 •  increases from p+p to central Au+Au at lower pT(trig) • Higher pT(trig) flat across all centralities • Systematic error not assigned (fit range,  projection window) 3 < pT(trig) < 6 GeV

  28. STAR preliminary  : pT(trig) Dependence of Width • Broadening in Au+Au compared to p+p, d+Au • Difference grows with decreasing pT(trig) • All systems are consistent for largest pT(trig) bin [6<pT<12 GeV] • Systematic error not assigned (fit range,  projection window)

  29.    Extracting Near-Side Jet Yields d+Au, 40-100% • In Au+Au, jetlike correlation sits on top of an additional, ~flat correlation in  • : cannot differentiate between the two correlations •  : additional correlation gets grouped into subtracted background STAR preliminary Au+Au, 0-5% 3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)

  30.  : pT(trig) Dependence of Correlated Yield • Gaussian areas consistent within errors for all pT(trig) • Yield growth with pT(trig): more assoc. particles for higher-pT parton • Correlation yield preserved despite broadening of correlation STAR preliminary widths from previous slide

  31. pTassociated varies pTtrigger varies Two-Particle Correlations in d+Au STAR preliminary STAR preliminary Background-subtracted correlations between a high-pT trigger charged particle and an associated charged particle

  32. STAR preliminary STAR preliminary Photon-Charged Particle Correlations in d+Au pTassociated varies ETtrigger varies See talk by Jana Bielcikova, today HT trigger sample Triggering with the STAR barrel and endcap EMC’s gives extended reach for correlation studies with high ET photons

  33. Forward Particle Production in d+Au Collisions BRAHMS, PRL 93, 242303 Difficult to explain with standard shadowing, but in NLO pQCD calculations <xg> ~ 0.02 for the BRAHMS data is not that small (Guzey, Strikman, and Vogelsang, PL B603, 173) Sizable suppression in charged hadron production in d+Au collisions relative to p+p collisions at forward rapidity

  34. √s=23.3GeV √s=52.8GeV Data-pQCD difference at pT=1.5GeV 2 NLO calculations with different scale: pT and pT/2 Ed3s/dp3[mb/GeV3] Ed3s/dp3[mb/GeV3] q=6o q=10o q=15o q=53o q=22o xF xF Do we understand forward π0 production in p + p? Bourelly and Soffer, EPJ C36, 371: NLO pQCD calculations underpredict the data at low s from ISR Ratio appears to be a function of angle and √s, in addition to pT

  35. STAR Forward π0 Inclusive Cross Section • STAR data at • = 3.8 (PRL 92, 171801) • = 3.3 (hep-ex/0403012, Preliminary) • NLO pQCD calculations at fixed  with equal factorization and renormalization scales = pT • Solid and dashed curves differ primarily in the g   fragmentation function STAR data consistent with Next-to-Leading Order pQCDcalculations -- in contrast to data at lower s

  36. STAR Fixed h, as E & pT grows Correlations in d+Au • are suppressed at small <xF> and <pT,p> • Spp-SdAu= (9.0 ± 1.5) % • Consistent with CGC picture • are consistent in d+Au and p+p at larger <xF> and <pT,p> • as expected by HIJING STAR Preliminary STAR Preliminary 25<Ep<35GeV STAR Preliminary STAR Preliminary 35<Ep<45GeV Statistical errors only

  37. Conclusions • Jet quenching, elliptic flow, and di-hadron correlations are all very similar in 62 GeV Au+Au to the results from 200 GeV Au+Au • Meson-baryon differences are also present in d+Au and 62 GeV Au+Au at intermediate pT • The saturation picture is consistent with back-front asymmetries and forward-midrapidity correlations in d+Au • Not all of the near-side associated hadrons are part of “the jet”. What are the rest?

  38. STAR The Collaboration Solenoid Tracker At RHIC 522 collaborators 51 institutions 12 countries

  39. In the soft sector... • (, ) space for low pT (< 2 GeV) studied extensively in STAR • Broadening of near-side  distribution in central Au+Auattributed to mini-jets • Evidence for longitudinal expansion •  width decreases slightly from peripheral to central central Au+Au, 130 GeV peripheral central peripheral STAR, nucl-ex/0411003, submitted to PRL

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